Multi-antenna technology has attracted attention as one of transmission schemes that can innovatively improve the channel capacity of a wireless communication system. If a base station is aware of instantaneous CSI of a mobile station, Singular Value Decomposition (SVD)-based techniques or single beamforming-based techniques can be used in a single user environment, and Dirty Paper Coding (DPC)-based techniques or multi-beamforming-based techniques can be used in a multi-user environment, which can provide improved system capacity.
Generally, in order to employ such a multi-antenna technology, a mobile station estimates the CSI using a pilot signal received together with data signal, transmitted from the base station, quantizes the CSI into a fixed bit size format, and reports the quantized CSI to the base station through an uplink channel.
In order to reduce the total amount of CSI information to be reported, a number of techniques for quantizing instantaneous CSI have been proposed. However, previous CSI quantization techniques still suffer from large signaling burden associated with frequent transmission of instantaneous CSI at each frame.
In order to alleviate such a problem, single- or multi-eigen-beamforming techniques have been proposed, which can improve the system capacity by generating transmit beams using channel correlation information which may represent the average (or statistical) CSI of a mobile station. Since the channel correlation is very slowly time-varying, such techniques are advantageous in that the mobile stations can report their channel correlation information to the base station at relatively long period, thus significantly reducing the CSI signaling burden.
However, previous studies show that the use of channel correlation information quantized into a small bit size may significantly limit the performance of multi-antenna technique. It is preferable to employ a quantization technique that can reduce the total amount of quantized channel information compared to existing schemes without degrading the system capacity, or can improve the performance by using the same amount of quantized channel information.